CAPE CANAVERAL — Shuttle astronauts hope to save a multimillion-dollar satellite today when they use Discovery's robot arm to reach out and snare the dead spacecraft with a homemade plastic hook worth a few cents.

Two rigged-up hooks, made from plastic book covers, were attached to the remote-controlled arm Tuesday by astronauts Jeffrey Hoffman and David Griggs during a three-hour spacewalk in Discovery's cargo bay. It was the first unrehearsed spacewalk in 16 shuttle flights.

If one of the hooks can be maneuvered to jerk open a lever and bring the satellite to life, NASA could win a customer's gratitude and a public relations coup in its competition with the French for satellite-launching business.

Work to save the Leasat satellite probably will postpone Discovery's landing at Kennedy Space Center until Friday morning, but space agency officials said they may aim for a Thursday touchdown.

The Leasat, which is insured for nearly $85 million, is being leased by the Navy for military communications. Its rocket engine failed to start just after rolling out of the cargo bay Saturday.

The 4-inch lever should have flipped outward, causing switches inside to start a sequence of events that would have led to the firing of the satellite's rocket motor 45 minutes later. The motor would have carried the satellite to a higher orbit.

Technicians said they believe the lever didn't open all the way, and Discovery crew members hope to confirm that when they move in close today. If the lever isn't partly sticking out they won't have anything to snare.

Floating near a spinning satellite and snaring the lever ''is not an easy task, yet we have confidence the job can be done,'' said flight director Jon Cox.

However, the shuttle will have to move away fast once the lever is pulled. Discovery, which was 40 miles from the satellite Tuesday, was to start its rendezvous maneuvers about 4:30 this morning and pull in beside the Leasat three hours later.

The shuttle will stay nearby for a 90-minute orbit of Earth before astronaut Rhea Seddon tries to snare the lever in one of three holes in each of the hooks, which resemble flyswatters.

She will have only 6 1/2 minutes -- 13 spins of the satellite -- to make the snare as the Leasat crosses the equator above the Atlantic Ocean. If she misses, the crew will wait for one more 90-minute orbit and try again, Cox said.

If one of the hooks rips she can use the other.

Crew members Monday fashioned the tools out of report covers, tape, tubing, window-shade rods and other things found aboard Discovery.

Although the Leasat is equipped with a type of rocket engine used by Minuteman ICBMs, Cox said there is little risk to the crew and Discovery, Cox said.

Shuttle astronauts showed their resourcefulness and skill Tuesday when Hoffman and Griggs attached the hooks to the arm in an unrehearsed procedure that went ''exactly as we hoped it would,'' Cox said.

The spacewalkers left the shuttle airlock about 7:30 a.m. and headed for tool boxes beneath the cargo bay floor.

Bathed in lights, they began to wrap a strap around the end of the robot arm, which is about 14 inches in diameter. The straps are aboard for tying down payloads.

The sun came up as the shuttle was passing south of California, giving the orbiter a bluish hue.

''Okay, the flyswatter is in the straps. I'll turn it the way I think you want it,'' Hoffman told ground controllers who were watching the operation closely on TV monitors.

Like flower arrangers, the two pushed and pulled the flyswatters in and out and tugged the straps into proper position before tightening the entire configuration into place.

''Is that beautiful, or is that not beautiful?'' Hoffman asked.

''That looks good,'' said Griggs. ''Go ahead, tighten it up.''

Ground technicians asked crew members inside Discovery to move the arm and change cameras several times to give a clear view of the spacewalkers' handiwork and to ensure that the arm would fit properly back into the cargo bay.

Then ground communicator Jerry Ross asked Hoffman and Griggs to stay floating in the bay a while longer until the shuttle came within television contact again for more inspection pictures.

''I'm sure you know how hard that's going to be,'' Hoffman joked.

After cleaning up, the two took a bow and were applauded from the ground before re-entering Discovery about 10:30 a.m.

During the afternoon, Seddon prepared for this morning's snare operation by conferring by radio with astronaut Sally Ride, who had tried the maneuver in a simulator at Johnson Space Center in Houston.

If the crew can bring the Leasat to life it will save time and trouble for the owner, Hughes Communications Inc., and should keep insurance costs from increasing.